However, later experiments showed a weakening or even disappearance of the shell effects associated with magic numbers in closed-shell nuclei away from \(\beta \) -stability.
Thibault et al. [1]} first reported the observation of the disappearance of the magic number (\(N=20\) )
based on mass measurements of the neutron-rich nuclei \(^{31,32}\) Na.
Later on, similar observations were made in several other neutron-rich nuclei around \(N=20\)  [2]}, [3]}, [4]}, [5]}, [6]},
indicating strong deviations of the shell ordering compared to the standard shell model [7]}.
